Microstructure device with an improved anchor

ABSTRACT

The present disclosure provides a system of fabricating a microstructure device with an improved anchor. A method of fabricating a microstructure device with an improved anchor includes providing a substrate and forming an oxide layer on the substrate. Then, a cavity is etched in the oxide layer, such that the cavity includes a sidewall in the oxide layer. A microstructure device layer is then bonded to the oxide layer over the cavity. Forming a microstructure device, a trench is etched in the device layer to define an outer boundary of the microstructure device. In an embodiment, the outer boundary is substantially outside of the sidewall of the cavity. Then, the sidewall of the cavity is etched away through the trench in the device layer, to thereby suspend the microstructure device over the cavity.

BACKGROUND

The present disclosure relates generally to semiconductor manufacturing.Specifically, the present disclosure relates to fabricating amicrostructure device with an improved anchor having a reduced undercut.

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. In the course of IC evolution, functionaldensity (i.e., the number of interconnected devices per chip area) hasgenerally increased while geometry size (i.e., the smallest componentthat can be created using a fabrication process) has decreased.

Microelectromechanical systems (MEMS) devices are very smallelectro-mechanical systems incorporated into semiconductor IC circuits.One example of a MEMS device is a micro-inertial sensor/accelerometer.Conventional silicon on insulator (SOI) type MEMS devices are fabricatedusing a buried oxide layer as a sacrificial material layer. As such, aportion of the oxide layer is removed at a later stage of fabrication torelease the MEMS device. Generally, the amount of oxide to be removed istime controlled where the etch time depends on the physical dimensionsof the MEMS device. Because the oxide etches uniformly, the oxide isremoved both from under the MEMS device and laterally from undersupporting structure, such as the anchor. This causes an undercutproblem for the anchor, which can weaken the anchor. The etching isusually performed from outside edges of the MEMS device and thus, theundercut of the anchor is approximately half of the dimension of theMEMS device. The undercut reduces strength of the anchor. To combat thislarge undercut problem, designers may perform an etch process of theoxide layer through the MEMS device using a number of releaseholes/trenches through the MEMS device to allow the etchant to etch theoxide layer beneath the MEMS device more quickly by etching frommultiple areas. However, this type of etching compromises the MEMSdevice by limiting device design flexibility and degrading deviceperformance (e.g., reducing total mass of a MEMS accelerometer).

Therefore, what is needed is a system of fabricating a microstructuredevice with an improved anchor.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flow chart illustrating an embodiment of a method offabricating a microstructure device with an improved anchor.

FIGS. 2-6 show cross-sectional and plan views illustrating an embodimentof a microstructure device according to the method of FIG. 1 at variousstages of fabrication.

FIGS. 7-10 show cross-sectional and plan views illustrating anembodiment of another microstructure device according to the method ofFIG. 1 at various stages of fabrication.

DETAILED DESCRIPTION

The present disclosure relates generally to semiconductor manufacturing.Specifically, the present disclosure relates to a system of fabricatinga microstructure device with an improved anchor. In an embodiment, thepresent disclosure provides a microelectromechanical system (MEMS)microstructure semiconductor device, such as amicro-inertial/accelerometer sensor. In one embodiment, the presentdisclosure provides a complementary metal oxide semiconductor (CMOS)chip having reduced undercut for the anchor. Using the methods describedherein the device's operating characteristics and physical structure areenhanced with respect to traditional devices.

It is understood, however, that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Furthermore, descriptions of a first layer “on,” “overlying,” (and likedescriptions) a second layer includes embodiments where the first andsecond layer are in direct contact and those where one or more layersare interposing the first and second layer. The present disclosurerefers to MEMS devices; however, one of ordinary skill in the art willfind other applicable technologies that may benefit from the disclosuresuch as, nanoelectromechanical systems (NEMS) devices, applicationspecific integrated circuit (ASIC) devices, and other such devices.Furthermore, the MEMS device structure or design illustrated isexemplary only and not intended to be limiting in any manner.

FIG. 1 is a flow chart illustrating an embodiment of a method 100 offabricating a microstructure device with an improved anchor.Cross-sectional views of different embodiments of such microstructuredevices are shown in FIGS. 2-10 at stages of fabrication. The presentdisclosure is described herein with respect to embodiments shown inFIGS. 2-10 relating to the method 100 provided in FIG. 1. The method 100provides for a microstructure semiconductor fabrication process. One ofordinary skill in the art would recognize additional steps that may beincluded in the method 100 and/or omitted from the method 100. Themethod 100 and the corresponding FIGS. 2-10 are exemplary only and notintended to be limiting. For example, the structure of the MEMS devicesdepicted in the figures are exemplary only and similar methods may beused to form other devices. CMOS circuitry may be included in thedevices depicted in FIGS. 2-10.

Accordingly, as should be understood by those having ordinary skill inthe art, the present disclosure provides embodiments of a microstructuredevice (e.g., a microelectromechanical systems (MEMS) device) withoutrelease holes through the microstructure device and with a shorterundercut under the anchor. In an embodiment, a buried insulatingisolation layer is patterned and etched to form a cavity. The size andshape of the cavity includes cavity walls under a device layer, in whicha microstructure device is formed. Then, in a subsequent release etchprocess for releasing the microstructure device, an etch process simplyneeds to etch away the walls of the cavity (and optional pillars), whichsupport the microstructure device, instead of having to etch a bulk filmunder the entire microstructure device. Thus, the etching process is ashorter time period. In other words, because the oxide layer etchprocess etches the oxide layer uniformly as long as the etchant ispresent, the oxide under both the anchor and the microstructure deviceis etched away. For example, if etchant etches the oxide layer from aperimeter of the microstructure device, the etchant conventionallyetches inward and outward the same distance under the anchor as underthe microstructure. If etchant is applied from opposite sides of themicrostructure device, the etched undercut under the anchor is one-halfthe distance of the length of the microstructure device (because theetching under the microstructure device comes from multiple sides).Therefore, if a shorter etch period is used because only the cavitywalls (and optionally pillars) need to be etched to release themicrostructure device, there is less etching time to etch an undercutunder the anchor. As a result, the undercut under the anchor is reduced.As should also be understood, a microstructure device having a smallundercut creates a larger, stronger anchor for the microstructuredevice.

FIGS. 2-6 are cross-sectional views illustrating an embodiment of amicrostructure device 200 according to the method 100 of FIG. 1 atvarious stages of fabrication. The method 100 begins at block 102 wherea substrate 201 (FIG. 2) is provided.

In an embodiment, the substrate 202 is an undoped silicon (Si), highresistance, substrate of any thickness. In an embodiment, the substrate202 has an approximate resistivity >3000 Ohm-cm. In an embodiment, thesubstrate 202 may include a bonded silicon on insulator (SOI) substrate.The substrate 202 may be crystalline Si or poly Si. In alternativeembodiments, the substrate 202 may include other elementarysemiconductors such as germanium, or may include a compoundsemiconductor such as, silicon carbide, gallium arsenide, indiumarsenide, and indium phosphide. One or more isolation features (notshown) may be formed on the substrate 202. The substrate 202 may alsoinclude one or more integrated circuit devices (not shown), such as CMOSdevices, (e.g., NMOS and/or PMOS transistors). The substrate 202 mayinclude circuitry associated with the transistors such as interconnectlayers (e.g., metal lines and vias) and interlayer dielectric layers(ILD).

The method 100 then proceeds to block 104 where an oxide layer 204(e.g., a buried oxide layer) is formed on the wafer substrate 202 (FIG.2). In an embodiment, the buried oxide layer 204 is a silicon oxide(SiO2) layer having a thickness range of approximately 1 um-3 um. Theburied oxide layer 204 may include a nitride layer to improve isolation.For example, in an embodiment, the oxide layer 204 may compriseSiN4/SiO2. In another embodiment, the oxide layer 204 may comprisepolysilicon/SiO2. In yet another embodiment, the oxide layer 204 maycomprise SiO2/polysilicon/SiO2.

The method 100 next proceeds to block 106 where the oxide layer 204 isetched to form a patterned cavity 206 (FIGS. 3 A&B) in the oxide layer204. View B of FIG. 3 is a plan view of an embodiment of the device 200showing a top view of the cavity 206 as an open cavity. View A of FIG. 3is a sectional view along lines A-A of view B showing a side view of thedevice 200. The etching process essentially removes the oxide layer 204down to the substrate layer 202 for the desired pattern of the cavity206. The etching process leaves a cavity sidewall/shoulder 208 in theoxide layer 204 to support a microstructure device, as is described inmore detail below. The cavity 206 is formed by patterning the oxidelayer 204 to a desired pattern using a photolithography process and thenperforming a wet etching process or by forming a dry plasma etchingprocess to the oxide layer 204. In an embodiment, the cavity 206 extendsthrough the oxide layer 204 to the substrate 202, however, this isoptional and the cavity 206 may not extend entirely through the oxidelayer 204 and alternatively, may extend through the oxide layer 204 andpart way into the substrate 202. Size dimensions for the cavity 206 maybe any size to accommodate a microstructure device (e.g., a MEMS device)formed above the cavity 206, as is described below.

After etching the cavity 206, the method 100 proceeds to block 108 wherea device layer 210 wafer is bonded to the oxide layer 204 over thecavity 206 (FIG. 4). In an embodiment, the device layer 210 is a dopedsilicon (Si), low resistance, substrate having a thickness range ofapproximately 5 um-40 um. In an embodiment, the device layer 210 has anapproximate resistivity <1 Ohm-cm. In an embodiment, the device layer210 may include a bonded silicon on insulator (SOI) substrate. Thedevice layer 210 may be crystalline Si or poly Si. In alternativeembodiments, the device layer 210 may include other elementarysemiconductors such as germanium, or may include a compoundsemiconductor such as, silicon carbide, gallium arsenide, indiumarsenide, and indium phosphide. One or more isolation features may beformed on the device layer 210. The device layer 210 may also includeone or more integrated circuit devices (not shown), such as CMOSdevices, (e.g., NMOS and/or PMOS transistors). The device layer 210 mayinclude circuitry associated with the transistors such as interconnectlayers (e.g., metal lines and vias) and interlayer dielectric layers(ILD).

In an embodiment, the device layer 210 is fusion bonded to the oxidelayer 204. The bonding process parameters depend on metal patterndensity and material properties. In an embodiment, a typical bondingtemperature is approximately room temperature (e.g., 20 C) toapproximately 200 C. Bonding force may be less than 5 kN and bondingtime may be less than 10 minutes. However, it should be understood thatother parameters may be used for the bonding.

Additionally, the method may include an optional grinding/formingprocess in block 108 to pre-form a microstructure device over the cavity206. This process may shape and/or thin the device layer 210 over thecavity 206 to put the microstructure in a form for performing theintended function of the microstructure device, such as an inertiasensor, a pressure sensor, and etc. The method may also include anoptional process to form a top oxide layer (e.g., SiO2) (not shown) onthe device layer 210 in block 108. In an embodiment, the top oxide layeris grown on the device layer 210 using a thermal oxidation heat process.In another embodiment, the top oxide layer is deposited on the devicelayer 210 using a chemical vapor deposition (CVD), plasma enhanced CVD,spin-on, sputter, or other depositing process for forming dielectriclayers on a substrate.

The method 100 proceeds to block 110 where the device layer 210 isetched to form a trench 212 around a perimeter of the microstructuredevice 214 to define outer boundaries of the microstructure device 214(FIG. 5). In an embodiment, the etch process, includes aphotolithography mask to define the desired etch pattern, such asdefining the trench 212. In an embodiment, the etch process performed onthe device layer includes a deep reactive ion etch (DRIE) process toetch the silicon of the device layer 210. The etching processes mayinclude a wet etching process, a dry plasma etching process, and/orother etching processes suitable for forming trenches to define themicrostructure device 214. It should be understood that a DRIE processmay include an anisotropic etching process capable of forming deep holesand trenches having aspect ratios of 20:1 or more. The DRIE process mayinclude cryogenic or Bosch etching processes. As shown in FIG. 5, thecavity sidewalls 208 extend under the microstructure device 214 andsupport it thereon. Thus, the outer dimensions for the cavity 206 aresmaller than corresponding dimensions for the microstructure device 214.Thus, after the etching process is completed to define the trench 212,there is very little oxide layer 204 left to remove to release themicrostructure device 214. As such, the etching process to remove thesidewalls 208 is a much shorter time period than conventional etchprocesses where a bulk film oxide layer under the entire length of themicrostructure device is removed.

Accordingly, the method 100 proceeds to block 112 where an etch processis performed through the trench 212 to etch away the sidewalls 208 ofthe cavity 206 and thus, release the microstructure device 214 (FIG. 6).In an embodiment, this etching process is performed using aphotolithography mask. The photolithography mask may be the same maskdiscussed above with respect to block 110 used to form the trenches 212.The etching processes may include a wet etching process, a dry plasmaetching process, and/or other etching processes suitable for etchingsilicon oxide layers. After the etching process, the trenches extenddown to the substrate 202. It should be understood that the etchingprocesses of blocks 110 and 112 may be performed as a single process ormultiple processes. As should be understood, the microstructure device214 is supported by the anchor 218 and related structurethree-dimensionally into or out of the device 200 (e.g., in front ofand/or in back of the sectional views shown in the figures). For examplesupport springs (not shown) may couple the microstructure 214 to theanchor 218 and allow the microstructure 214 to flex without breaking. Inan embodiment, the etching includes a vapor HF etching process or an HFwet etching process. In an embodiment, a typical vapor HF etchingparameters are approximately (e.g., 20 C) to approximately 100 C.Chamber pressure may be approximately 50-250 mbar. Etching time dependson device size.

As should be understood, the etch process of block 112 etches away atthe oxide layer 204 substantially uniformly in all directions.Therefore, the oxide layer 204 is etched laterally along the oxide layer204, removing the cavity sidewall 208 below the trench 212 and into thecavity 206. In addition, the etch process etches away an undercutportion 216 of the oxide layer 204 under an anchor 218 portion of thedevice layer 210. Because the etch process only needs to etch away theside walls 208 of the cavity, the etch process is performed during amuch shorter time period than conventional microstructure fabricationprocesses. Therefore, the etching to the undercut area 216 of the anchoris much less using the method 100 than using conventional microstructureprocesses. In an embodiment, the lateral length dimension of theundercut 216 is less than half of the lateral length dimension of themicrostructure device 214. In an embodiment, the cavity 206 has a sizedimension of less than 1 mm×1 mm. The trench 212 may be formed to beapproximately 0.2 um to approximately 10 um. In an embodiment, themicrostructure device 214 has a size dimension of less than 1 mm×1 mm.The undercut 216 may be formed to be less than approximately 2 um.However, it should be understood that other dimensions may be used.

The method 100 next proceeds to block 114 where the device 200 ispackaged to protect the device 200. The device 200 may also include atop cap CMOS wafer (not shown) bonded to the device 200, therebycreating a hermetically sealed package and CMOS integrated circuitdevice. The CMOS wafer may include a number of metal (e.g., Al, Cu,etc.) pads formed on the wafer using traditional CMOS processes. Themetal pads are bonded to the device 200 using a eutectic bond process.In an embodiment, the pads electrically couple with circuitry, such as adriver circuit, on the CMOS wafer, thereby providing electrical couplingwith other portions of the microstructure device 200. In addition, theCMOS wafer may include a contact pad, which couples circuitry in thedevice 200 outside of the device 200. The device 200 may be enclosed ina package and top cap assembly where the package is formed using amolding process and may include an epoxy coating. In an embodiment, thetop cap is configured to be a printed circuit (PC) board package. Thepackage assembly may include a wire bond coupling the contact pad to anoutside contact on the top cap. As should be understood, packaging ofthe device 200 provides for increased protection of the device 200.

As should be readily understood, the device 200 may include apiezoelectric transducer or other MEMS type device formed into or bondedto (not shown) the microstructure device 214. In an embodiment, atransducer may include a bottom metal layer, a piezoelectric layer and atop metal layer. The metal layers may include Al, Pt, Mo, AlCu, Ti, andcombinations thereof. The piezoelectric layer may include AlN, PZT,and/or ZnO. However, other materials may be used for the metal layersand the piezoelectric layers. The transducer may be fabricated on orotherwise bonded to the microstructure device 214 before the oxiderelease below the microstructure device 212 described in block 112. Thelayers of the piezoelectric transducer may be formed using a sputterdeposition or other process. The usefulness of the device 200 describedabove with respect to method 100 should be readily understood by thosehaving ordinary skill in the art.

FIGS. 7-10 show cross-sectional and plan views illustrating anembodiment of another microstructure device 300 according to the method100 at various stages of fabrication. The devices shown in FIGS. 7-10described below may be fabricated, in part, using the method 100 and mayhave features substantially similar to that of device 200. Accordingly,features and processes, which are similar to those described for device200 are not duplicated here for simplicity.

FIG. 7 shows an alternative microstructure device 300 having an improvedanchor and relates to block 106 of method 100 where the oxide layer 204is etched to form a patterned cavity 306 (FIGS. 7 A&B) in the oxidelayer 204 having a plurality of pillars 318. View B of FIG. 7 is a planview of an embodiment of the device 300 showing a top view of the cavity306 having the plurality of pillars 318 formed in the cavity 306. View Aof FIG. 7 is a sectional view along lines A-A of view B showing a sideview of the device 300. The etching process essentially removes theoxide layer 204 down to the substrate layer 202 for the desired patternof the cavity 306. The etching process leaves a cavity sidewall/shoulder208 in the oxide layer 204 to support a microstructure device 214. Thecavity 306 is formed by patterning the oxide layer 204 to a desiredpattern using a photolithography process and then performing a wetetching process or by forming a dry plasma etching process to the oxidelayer 204. In an embodiment, the cavity 306 extends through the oxidelayer 204 to the substrate 202, however, this is optional and the cavity306 may not extend entirely through the oxide layer 204 andalternatively, may extend through the oxide layer 204 and part way intothe substrate 202. Size dimensions for the cavity 306 may be any size toaccommodate a microstructure device (e.g., a MEMS device) formed abovethe cavity 306. In an embodiment, the pillars 318 have dimensions ofapproximately 0.5 um to approximately 4 um. However, other sizes ofpillars may be used.

FIG. 8 shows the microstructure device 300 and relates to block 108 ofmethod 100 where the device layer 210 wafer is bonded to the oxide layer204 (and the pillars 318) over the cavity 306. As should be understood,the plurality of pillars provides a greater bonding strength for bondingthe device layer 210 to the device 300. The bonding process issubstantially similar to that discussed above with respect to device 200in block 108.

FIG. 9 shows the microstructure device 300 and relates to block 110 ofmethod 100 where the device layer 210 is etched to form a trench 212around a perimeter of the microstructure device 214 to define outerboundaries of the microstructure device 214. The etching process issubstantially similar to that discussed above with respect to device 200in block 110.

FIG. 10 shows the microstructure device 300 and relates to block 112 ofmethod 100 where an etch process is performed through the trench 212 toetch away the sidewalls 208 of the cavity 306 and the pillars 318, andthus, release the microstructure device 214. The etching process issubstantially similar to that discussed above with respect to device 200in block 112. However, it should be understood that the etch process torelease the microstructure device 214 may need to be performed for atime period that is longer than that for device 200 in order to havetime to etch away the pillars 318 in the cavity 306. Accordingly, theundercut 316 may be proportionately longer than the undercut 216 fordevice 200. However, the undercut 316 should still be smaller than thatfor conventional microstructure devices fabricated using conventionalfabrication processes.

As should be understood the microstructure 212 may be formed as a MEMSdevice, in whole or in part. The MEMS device may include a plurality ofelements formed on metal, polysilicon, dielectric, and/or othermaterials. The MEMS device may include materials typically used in aconventional CMOS fabrication process. Any configuration of MEMS devicemay be possible, depending on the desired functionality. One or more ofthe elements depicted may be designed to provide MEMS mechanicalstructures of the MEMS device. The MEMS mechanical structures mayinclude structures or elements operable for mechanical movement. TheMEMS device may be formed using typical processes used in CMOSfabrication, for example, photolithography, etching processes (e.g., wetetch, dry etch, plasma etch), deposition processes, plating processes,and/or other suitable processes. In an embodiment, the MEMS device maybe a motion sensor (e.g., a gyroscope, an accelerometer, etc.), a radiofrequency (RF) MEMS device (e.g., an RF switch, filter, etc.), anoscillator, or any other MEMS type device. Various sizes of MEMS devicesare contemplated.

The MEMS device may be configured to interact with outside perturbation,such as temperature variation, inertial movement, pressure changes,and/or other electrical, magnetic, or optical parameter measurements.For example, in an embodiment, when the devices of the presentdisclosure are exposed to a pressure change, the MEMS devicemicrostructure 214 will deform inward or outward and thus, a sensingsignal will be created to indicate a pressure change. It is noted thatthe portions of the CMOS wafer may include one or more circuit devices(not shown), such as transistors (e.g., NMOS and/or PMOS transistors).The CMOS wafer may also include circuitry associated with thetransistors, such as interconnect layers (e.g., metal lines and vias)and interlayer dielectric layers (ILD). As should be understood,conductors on the device 200 may be mounted directly onto a printedcircuit board (PCB) using surface-mount or other technology processes.

The present disclosure provides for many different embodiments. In oneembodiment, the present disclosure describes a system of fabricating amicrostructure device with an improved anchor. A method of fabricating amicrostructure device with an improved anchor includes providing asubstrate and forming an oxide layer on the substrate. Then, a cavity isetched in the oxide layer, such that the cavity includes a sidewall inthe oxide layer. A microstructure device layer is then bonded to theoxide layer over the cavity. Forming a microstructure device, a trenchis etched in the device layer to define an outer boundary of themicrostructure device. In an embodiment, the outer boundary issubstantially outside of the sidewall of the cavity. Then, the sidewallof the cavity is etched away through the trench in the device layer, tothereby suspend the microstructure device over the cavity.

In another embodiment, the present disclosure provides a method offabricating a microstructure device. The method includes providing asubstrate and forming an oxide layer on the substrate. After forming theoxide layer, the method includes etching a patterned cavity in the oxidelayer by forming a photoresist pattern on the oxide layer. The patterndefines a sidewall around a perimeter of the cavity and a plurality ofpillars within the cavity. The pillars remain in the cavity after theetching of the patterned cavity. The method then includes bonding amicrostructure device layer to the oxide layer and the plurality ofpillars, over the patterned cavity. After the microstructure devicelayer is bonded, the method includes etching a trench in the devicelayer to define an outer boundary of a microstructure device. In anembodiment, the outer boundary is outside of the sidewall of the cavity.Then, the method includes etching away the sidewall of the cavity andthe plurality of pillars through the trench in the device layer,creating an open cavity, thereby suspending the microstructure deviceover the open cavity.

As an example, yet another embodiment of the present disclosure providesa microelectromechanical system (MEMS) device having an improved anchor.The device includes a substrate, and an oxide layer formed on thesubstrate, a cavity etched in the oxide layer. The device furtherincludes a microstructure device layer bonded to the oxide layer, overthe cavity. The microstructure device layer includes a substantiallysolid microstructure MEMS device formed in the microstructure devicelayer and is suspended over a portion of the cavity. An anchor is formedin the device layer and is configured to support the microstructuredevice, the anchor has an undercut in the oxide layer. In an embodiment,the undercut has a length along the anchor that is less than one-half alength of an outer boundary dimension of the microstructure MEMS device.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A method of fabricating a microstructure devicewith an improved anchor, the method comprising: providing a substrate;forming an oxide layer on the substrate; etching a cavity in the oxidelayer, such that the cavity includes a sidewall in the oxide layer;bonding a microstructure device layer to the oxide layer, over thecavity; etching a trench in the device layer to define an outer boundaryof a microstructure device, wherein the outer boundary is outside of thesidewall of the cavity; and etching away the sidewall of the cavitythrough the trench in the device layer, thereby suspending themicrostructure device over the cavity.
 2. The method of claim 1, furthercomprising forming an anchor in the device layer to support themicrostructure device.
 3. The method of claim 2, wherein the etchingaway the sidewall of the cavity creates an undercut below the anchor inthe oxide layer, the undercut being formed to have a length along theanchor that is less than one-half a length of the outer boundary of themicrostructure.
 4. The method of claim 1, further comprising forming themicrostructure device as a microelectromechanical system (MEMS) device.5. The method of claim 1, wherein the forming the oxide layer on thesubstrate includes forming the oxide layer as a silicon oxide layer. 6.The method of claim 5, wherein the etching away the sidewall of thecavity through the trench includes etching the silicon oxide layer usinga vapor or a wet etch process.
 7. The method of claim 1, furthercomprising hermetically sealing the microstructure device in a package.8. A method of fabricating a microstructure device, the methodcomprising: providing a substrate; forming an oxide layer on thesubstrate; etching a patterned cavity in the oxide layer, by forming aphotoresist pattern on the oxide layer, wherein the pattern defines asidewall around a perimeter of the cavity and a plurality of pillarswithin the cavity, which remain after the etching of the patternedcavity; bonding a microstructure device layer to the oxide layer and theplurality of pillars, over the patterned cavity; etching a trench in thedevice layer to define an outer boundary of a microstructure device,wherein the outer boundary is outside of the sidewall of the cavity; andetching away the sidewall of the cavity and the plurality of pillarsthrough the trench in the device layer, creating an open cavity, therebysuspending the microstructure device over the open cavity.
 9. The methodof claim 8, further comprising forming an anchor in the device layer tosupport the microstructure device.
 10. The method of claim 9, whereinthe etching away the sidewall of the cavity creates an undercut belowthe anchor in the oxide layer, the undercut being formed to have alength along the anchor that is less than one-half a length of the outerboundary of the microstructure.
 11. The method of claim 8, furthercomprising forming the microstructure device as a microelectromechanicalsystem (MEMS) device.
 12. The method of claim 8, wherein the forming theoxide layer on the substrate includes forming the oxide layer as asilicon oxide layer.
 13. The method of claim 12, wherein the etchingaway the sidewall of the cavity through the trench includes etching thesilicon oxide layer using a vapor or a wet etch process.
 14. The methodof claim 8, further comprising hermetically sealing the microstructuredevice in a package.
 15. A microelectromechanical system (MEMS) devicecomprising: a substrate; an oxide layer formed on the substrate; acavity etched in the oxide layer; a microstructure device layer bondedto the oxide layer, over the cavity, the microstructure device layerincluding a substantially solid microstructure MEMS device formed in themicrostructure device layer and suspended over a portion of the cavity;and an anchor formed in the device layer and configured to support themicrostructure device, the anchor having an undercut in the oxide layer,the undercut having a length along the anchor that is less than one-halfa length of an outer boundary dimension of the microstructure MEMSdevice.
 16. The device of claim 15, wherein the oxide layer comprisessilicon oxide.
 17. The device of claim 15, further comprising a packagehermetically sealing the device from outside elements.
 18. The device ofclaim 15, wherein the MEMS device is configured as an accelerometer. 19.The device of claim 15, wherein the MEMS device is configured as agyroscope.
 20. The device of claim 15, wherein the MEMS device isconfigured as a piezoelectric resonator.